1. Field of the Invention
This invention relates to novel thermoformable compositions comprised of a crosslinked polycyanurate network polymer in which a high molecular weight thermoplastic polymer is finely dispersed.
2. Brief Description of the Prior Art
Thermoplastic polymers, having a high glass transition temperature, are useful in a variety of industrial applications including the manufacture of many molded and shaped articles. For example, polyestercarbonates, a known class of thermoplastic polymers, are especially useful for producing protective windshields and canopies having excellent impact resistance, low processing temperatures and good flexibility, as described in U.S. application Ser. No. 764,623, which is hereby incorporated by reference. However, products made from thermoplastic polymers generally have the disadvantage of possessing marginal abrasion resistance and solvent resistance, under specific conditions, for example, such as contact with boiling solvent.
Crosslinked polymers, for example, polycyanurates (crosslinked cyanurate polymers) derived by the polycyclotrimerization of aromatic cyanates, are known to produce shaped articles possessing excellent hydrolytic and solvent resistance. However, the articles have low yield strength and poor flexibility. See for example, U.S. Pat. No. 4,026,913 of May 31, 1977 assigned to Mitsubishi Gas Chemical Co. at col. 1, lines 8-16, which describes cyanic acid esters of aromatic polycarbonates which can be cured to produce crosslinked polycyanurates. Also see the references, Kunststoffe, Bd. 58, pp. 827-832(1968) by R. Kubens et al., and Dokl, Akad. Nauk SSSR, Vol. 202, pp. 347-350 (1972) by V. V. Korshak et al., which describe the cyclotrimerization of aryl cyanurates and properties of crosslinked polymers derived therefrom. In addition, the references, U.S. Pat. No. 4,046,796 (1977) and German Offenlegungsschrifte Nos. 2,549,529; 2,546,296; and 2,546,315, describe processes for producing certain polyfunctional cyanic acid esters, e.g. from cyanuric acid chloride, hexamethylene diamine, bis-phenol-A, and cyanogen chloride, and cured products derived therefrom.
In general, blends made of physically distinct thermoplastic and crosslinked polymer compositions do not exhibit the combined desirable characteristics of both types of polymers due to a general inherent incompatibility of composition properties between the two types of polymers.
What is needed and what the prior art does not describe are substantially homogeneous compositions exhibiting the desirable characteristics of both thermoplastic and crosslinked polymer compositions and capable of forming shaped articles having excellent yield and impact strengths coupled with flexibility, thermal processability, good heat resistance and good solvent resistance.